An electric mower is provided with a blade motor for rotating a cutting blade, an electric control unit for controlling the blade motor, and a battery for powering the blade motor and the control unit. In such an electric mower, it is necessary to remove heat generated from the blade motor and the control unit. See US2003/037525A1, for instance. The mower may also be provided with a travel motor for driving the wheels, but the power of the blade motor may also be used for driving the wheels without requiring a travel motor.
The electric mower disclosed in US2003/037525A1 is provided with a cover member that covers the blade motor and the battery. The battery is positioned above the blade motor, and a control unit is interposed between the battery and the blade motor. The cover member defines an air inlet in a lower front part thereof, and air outlet in a rear part thereof. The air admitted from the air inlet is passed along the both sides of the blade motor and the battery in order to cool such parts.
When high performance electric motors consisting of brushless motors are used, it is highly important to remove heat from the control unit as well as from the electric motor. In the case of the electric mower disclosed in US2003/037525A1, because the control unit is vertically interposed between the electric motor and the battery, the air flow passing along both sides of these components may not produce a desired cooling effect.
In view of such a problem of the prior art, a primary object of the present invention is to provide an electric mower configured to favorably remove heat from an electric motor and a control unit thereof.
The present invention achieves such an object by providing an electric mower (1), comprising: a blade housing (2b) defining a cavity (7) opening out downward and a vertical passage (32) extending centrally upward from the cavity; a metallic motor support plate (38) attached to a part of the blade housing defining an upper end of the vertical passage and provided with an extension (42) extending beyond the vertical passage in a horizontal direction; an electric motor (8) attached to the motor support plate and having an output shaft (64) extending downward through an opening formed in the motor support plate; a blade (3) attached to a lower end of the output shaft and covered by the blade housing; and a control unit (10) mounted on an upper surface of the extension for controlling the electric motor.
The heat generated in the electric motor and the control unit is transmitted to the motor support plate, and is dissipated from the surface of the motor support plate so that the electric motor and the control unit can be favorably cooled.
A plurality of fins (84) may be provided on at least a part of a lower surface of the motor support plate.
By thus increasing the surface area of the motor support plate, the electric motor and the control unit can be particularly favorably cooled.
The fins may be provided on at least a part of a lower surface of the extension of the motor support plate.
The fins can be formed in a relative exposed part of the motor support plate without interfering with other components of the mower so that the cooling effect may be optimized.
The control unit may be attached to an upper surface of the part of the extension provided with the fins.
Since the control unit is typically most sensitive to overheating, it is advantageous to attach the control unit to the upper surface of the part of the extension provided with the fins.
According to a preferred embodiment of the present invention, the mower further comprises an upper housing (2a) attached to an upper end of the blade housing to define an air passage (A) in cooperation with an upper surface (30) of the blade housing; and the air passage communicates with the atmosphere via an air inlet (21) defined at least partly by the upper housing, and includes a space defined between the upper surface of the blade housing and at least a part of a lower surface of the extension.
Thereby, the fresh air admitted from the air inlet can be conducted through the space defined between the upper surface of the blade housing and at least a part of a lower surface of the extension so that the motor support plate, in particular the extension thereof, can be favorably cooled by the fresh air.
Preferably, fins aligning with a direction toward the air inlet are provided on at least a part of the lower surface of the extension.
Thereby, the cooling effect of the fins can be maximized.
The mower may further comprise a motor cover (67) attached to an upper surface of the motor support plate to define a chamber receiving the electric motor and the control unit therein.
Thereby, the electric motor and the control unit are protected from foreign matters such as dust and moisture so that the durability of the mower can be maximized. The motor cover may be made of plastic material so that the weight increase may be minimized.
Preferably, the air passage communicates with the vertical passage via a gap defined between the motor support plate and the upper surface of the blade housing.
Thereby, the air admitted from the air inlet is drawn into the cavity by the negative pressure created by the rotation of the blade so that a large amount of air may be passed through the air passage, and the electric motor and the control unit can be favorably cooled.
Preferably, the motor support plate is attached to the upper surface of the blade housing via a plurality of rubber bushes so that the rubber bushes create the gap by spacing the motor support plate from the upper surface of the blade housing.
The rubber bush not only insulate the vibrations of the electric motor from the remaining part of the mower but also contributes to the creation of the gap communicating the air passage with the cavity without requiring any other special component parts.
The electric motor may consist of a permanent magnet motor including a stator and a rotor, the stator being substantially in direct contact with the motor support plate.
Thereby, the heat generated in the electric motor can be favorably conducted to the motor support plate.
Preferably, the motor support plate is provided with an upper annular boss formed on an upper surface of the motor support plate, and a top end surface of the upper annular boss is substantially in direct contact with the stator.
Thereby, the heat transfer between the stator and the motor support plate can be maximized.
Preferably, the motor support plate is further provided with a lower annular boss formed on a lower surface of the motor support plate, and the output shaft of the motor is supported by a pair of bearings provided in the opening of the motor support plate in an axially spaced apart relationship.
By supporting the output shaft of the electric motor by two bearings that are axially spaced from each other, the rotor of the motor can be supported relatively to the stator in a stable manner by firmly resisting the tilting movement of the output shaft.
The present invention thus provides an electric mower configured to favorably remove heat from an electric motor and a control unit thereof.